Fiber gratings are well known and have been used for measuring axial and transverse loads. Applications of these fiber gratings have been used primarily to measure strain fields in composite materials and in adhesive joints. To measure transverse loads, some conventional sensors rely on embodiments that apply transverse load on an optical fiber. The transverse load induces differential strain across the optical core. This causes the optical core to manifest two different effective indices of refraction and two “effective” fiber gratings spaced relative to the induced index of refraction difference. These principals have been applied to measure transverse strain/load in a variety of applications.
There are a number of significant issues with the conventional sensors that measure transverse load. One issue is that the amount of birefringence induced by small to moderate transverse loads is very small. Significant efforts are required to accurately read out these differences and that in turn drives up cost. An alternative is to mechanically amplify the transverse load. This results in larger sensors, increased cost, and in some cases a need for high precision in alignment and fabrication methods. For some applications in which transverse load sensors are subject to high electrical fields, it is important to eliminate air gaps. This requirement makes it more difficult to employ some conventional geometries, including geometries utilizing side-hole optical fibers.